text:
Can a wing generate lift in excess of its aircraft's weight?
"For a plane or bird to fly, its wings must produce enough lift to equal its weight. "
I got that excerpt from "https://www.sciencelearn.org.nz/resources/300-wings-and-lift".
My questions:
(1) Can an aircraft wing create lift that is greater than the weight of the aircraft?
(2) If the answer to question (1) is yes, then what happens in such a situation?

The aircraft climbs. This implies that to fly higher than ground level a flying thing MUST generate lift in excess of its weight at least some of the time

It's not clear from your question that you understand the principles of flight. If lift was not greater than weight then how do you think an aircraft could rise in the air?

@Transistor: By having a thrust-to-weight ratio greater than 1 and pointing the engines downward, for example. (Yes, this is not aerodynamic lift, but you started your comment with the assumption that the OP doesn't understand lift, and then proceed to make an argument based on lift, so be prepared for that to … ahem … fly over their head.)

@Jörg W Mittag: Sure, but very few airplanes (or even helicopters) have their engines pointed downwards.  Of course neither propellor planes nor helicopters would get very far if their propellors/rotor blades (which are just specialized wings) didn't produce "lift".  And jet engines tend to have lots of little "wings" inside them...

@slebetman -- no, see -- https://aviation.stackexchange.com/questions/40921/does-lift-equal-weight-in-a-climb/56476#56476 -- "Clearly, Lift is less than Weight in a powered climb."

@Transistor -- see above comment

@jamesqf No need to go even that far - consider a glider, for example.  The only thing that lifts it is the wing.

Wow, we're still on this stuff.  1.  Most efficient way to climb is to use the wing.  Thrust horizontal, excess lift to create slightly less excess vertical lift.  2. Yes, planes can have thrust pointing downwards, it's called "downthrust", and is used to counteract pitch-up tendency created by increasing speed from steady state flight.  A condition of using less lift than weight to climb exists, but using thrust as part of the vertical component is generally less efficient.

@quietflyer That may be so but you would need to get into the climb which requires a change in climb rate which requires more lift than weight. Otherwise the aircraft will just stay with the current climb rate. Considering all aircraft starts on the ground with a climb rate of zero that means you need more lift than weight at some point regardless how it's produced - wings, rockets etc. For most planes it's the wings

Yes, a wing can (given sufficient forward speed and angle of attack) generate lift greater than the weight of the aircraft.  As with any "unbalanced" force, this will result in an acceleration of the airplane in the direction of the lift, according to Newton's Second law. $$\mathbf F=m~\mathbf a$$
Please note, the entities in bold face are vector quantities.
This is what happens during any positive $\mathrm G$ maneuver, like a pullout from a dive, a loop, etc.

Or even a simple take-off or climb.

@Ray: Strictly speaking the lift exceeds weight only while transitioning to a higher rate of climb; when a steady climb is achieved the lift matches the weight again.

@A.I.Breveleri In fact, because the engines are pointed somewhat downwards, the lift will actually be less than the weight.

To be even more precise, when the rate of climb is constant, be it positive or negative, some drag will be present on the up/down axis. When the climb is positive lift will need to be a bit higher than weight, to win this additional force.

@VladimirCravero That is true, and besides that the lift is also not aligned with gravity anymore. Lift is defined as being perpendicular to drag, not necessarily aligned with gravity. Altough it is usually the case, lift does not always have to be larger than gravity when climbing, some jet fighters are so powerful they can hang vertically in the air with almost no velocity and thus with nearly no lift.

@Orbit -- "Altough it is usually the case, lift does not always have to be larger than gravity when climbing," -- actually, it is usually not the case.  See https://aviation.stackexchange.com/questions/40921/does-lift-equal-weight-in-a-climb/56476#56476 -- "Clearly, Lift is less than Weight in a [wings-level] powered climb"

Yes, otherwise airplanes would be unable to go upwards into the sky.

Perfect case of reductio ad absurdum. I would rather use gliders to make it even more undisputable (the wings can lift the airframe even when no engine is helping).

I like the simplicity of this answer far more than the other answers. They make it sound far more complex than it is.

This answer is simple, but it's a bit oversimplified. It's entirely possible to climb without having lift > weight. Rockets, for example, use thrust instead of aerodynamic lift to counter the gravitational force. The simplest way to put it that is still completely correct would be to say, "In order for the aircraft to accelerate upwards, it must be able to, at least briefly, generate an upward force greater than its weight." Once the climb has been established, the net upward force can (and, in the case of an airplane, typically will) return to being equal to the weight.

@reirab Hence kuroi nekos suggestion.

Gliders generate lift, but except when coming out of a dive (with lots of speed), they only gain altitude when there's an updraft to take advantage of.  Sans motor/propeller, they can't generate airspeed (other than by diving)

See -- https://aviation.stackexchange.com/questions/40921/does-lift-equal-weight-in-a-climb/56476#56476 -- "Clearly, Lift is less than Weight in a powered climb."

But rockets aren't aircraft.

@reirab -- "Once the climb has been established, the net upward force can (and, in the case of an airplane, typically will) return to being equal to the weight."  -- but wing's lift (the subject of the original question) will be less than weight during that established climb.  See my previous comment to this answer for more.

@quietflyer Agreed. That's specifically why I said "net upward force" and not "lift." :)

I am torn between "This answer lacks enough detail to be a complete answer" and "This answer sums up the situation perfectly".

"Once rate of climb is established, net upward force can return to being equal to weight" negative, sorry, a climbing object will also have a vertical drag component.  Net upward force = weight + vertical drag.  Net upward force will consist of vertical thrust, vertical wing lift, or a combination of the two.  It will greatly benefit this site to get this squared away.

Furthermore to @Zeiss' answer, whenever an aircraft is steady-state banked, the lift will be greater than its weight. However, its speed will be constant; instead, the acceleration is centripetal and results in a circular turn.
Edit, clarification on pull up maneuver:
When an aircraft is pitched up via pitch control, and after the short-period mode settles (a few seconds at most), it will gain a lift imbalance greater than its weight due to higher angle of attack (AOA). Similar to a banked turn, since the net force is perpendicular to the horizontal velocity, it will be centripetal and results in a vertical circular motion. This is the early stage of the maneuver.
Since a higher AOA has higher drag, the airspeed will decay toward a new and lower trim speed. At the same time, as airspeed decreases, the net lift also decreases, so there is less force imbalance. As the decreasing airspeed undershoots the new trim speed, the aircraft will pitch down again. This cyclical exchange of energy is called phugoid and usually persists for a while (dozens of minutes to an hour) if left unchecked.
Eventually, however, the phugoid dies down (phugoid is usually stable in non-transonic regime) and the airplane is flying at the new trim speed, with lift equal to weight once again. If the airplane is in the front of the power curve, it will climb at steady-state; otherwise, it will descend.

A kite is a simple aircraft, generating lift. The vertical component of the pull you feel on the string is any resultant lift greater than the weight of the aircraft, the horizontal component being the drag. In a non-tethered aircraft, excess lift causes the aircraft to "rise", or more precisely, causes the flight path to curve upwards.

See -- https://aviation.stackexchange.com/questions/40921/does-lift-equal-weight-in-a-climb/56476#56476 -- "Clearly, Lift is less than Weight in a powered climb."

I've edited as per my suggestion.  You are welcome to roll back if you feel  the edit does not respect the intent of your answer.

@quietflyer the intent was to supplement the other answers' more theoretical descriptions with a physical sensation the OP may well know, as many people learn better that way, with all these comments it rather spoils the effect. Oh well.

Ok comments removed. If you want to roll it back all the way I'll leave it alone.

The lift a wing CAN generate is a design feature of the wing.
The lift a wing does generate is a feature of the weight and the flight path of the aircraft.

The first part is correct, but the second part is not.  Lift produced is a function of speed and angle of attack.  Weight does not contribute to generating lift, it is the opposing force that must be overcome by lift to fly.

In addition to what Michael said, flight path doesn't (directly) influence wing lift generation, either. Angle of attack (angle between air flow and wing chord line) does, though.

More than one way to skin a cat; I think the answer is fine.  If you know the weight and the flight path, then you know the lift.  Consider that the pilot (or autopilot) is also in the loop, manipulating the controls, and thus indirectly the angle-of-attack, to obtain the desired flight path.  Therefore it's arguably a true statement to say that "the lift a wing does generate is a feature of the weight and the flight path of the aircraft."   Is the statement claiming that flight path is CAUSING the lift rather than vice versa?  I'd say no.

If you have an aircraft with 20 tons of cargo, and the total weight of the aircraft, including cargo, is 60 tons, then clearly the wings are capable of producing 60 tons of lift. If you fly the same plane without cargo, then that's not going to affect the amount of lift the wings can produce. So clearly there are situations where the wings can produce more lift than the weight of the aircraft.
Something else that shows that aircraft must be sometimes operating below their maximum lift is that when an airplane takes off or lands, it's not moving at its maximum speed. Since lift increases with speed, that means that its lift is significantly crippled. If an airplane has enough lift to fly at runway speeds, then it has more than enough lift to fly at cruising speed.
In addition, an aircraft is going to need a margin to climb,  turn (one of the reasons airplanes bank when turning is that the lifting force of the wings can then be applied to centripetal force, aka turning the aircraft), etc. Tell any pilot that you want them to fly a plane with a maximum lift equal to, or only slightly above, the weight of the plane, and unless they have a death wish they'll be running the other way.

Some parts of your answer appear to be using "lift" to mean something more like "potential lift", meaning the amount of lift that would be generated at any given airspeed if we instantly snapped the wing to the max-lift angle-of-attack.  Does lift-- real lift, not "potential" lift-- really increase with airspeed?  If yes, then what are you holding constant, and what is the flight path that results?


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Would an oval fuselage fly as well as a round one?
I was looking at various planes, and was wondering why we don't have oval shaped fuselages instead of only round ones.  Is there a reason?  Perhaps aerodynamics, or stresses?

A fuselage circular cross-section is best for pressurization (weight). For non pressurized aircraft, circular is still best for sideslip drag (fuel). In both cases elliptical is preferred for volume, and actually most aircraft have an elliptical section. I think your questions are already answered in Why is the fuselage on an airliner circular-shaped? and Could some one explain me with the mathematical relations on how the double bubble fuselage cross section (example A380) is designed

@ymb1 Plenty of examples of circular cross sections, Boeing's marketing department made it a big deal on the 777 despite them being the last to the game. Round planes include the A300 and derivatives the A330/A340, Boeing 777, 787, DC-10, MD-11. Smaller planes like the EMB-120/ERJ145, CRJ-100/200. Forgotten round planes include the Mercure, Fokker VFW-614.

Perhaps the best known of airliners with an obviously not circular fuselage is the Boeing 747.  And if you get away from airliners, there are a lot of planes with non-circular cross sections, for instance a lot of WWII fighters.

Lots of early aircraft had square cross-sections because it was easier to build.

TL;DR: There are (primarily structural) reasons for circular fuselages... but there are also reasons to deviate somewhat from circularity, and many aircraft actually do have oval fuselages!
(Explanation partially cribbed from here.)
For a pressurised aircraft, a circular cross-section is indeed optimal from a stress standpoint, as it spreads out the pressurisation stresses evenly without any areas carrying a much higher stress than others.  Areas of high pressurisation-stress concentration are bad, because pressurisation imposes cyclical stresses (each time the aircraft takes off and ascends to cruising altitude, the pressure differential between inside and outside gradually increases,1 imposing increasing stress on the pressure hull; each time it descends from cruising altitude and lands, the pressure differential gradually decreases, eventually to zero, slowly releasing the stress on the pressure hull), cyclic stresses produce fatigue damage (something to which the aluminium alloys generally used in aircraft construction are unusually vulnerable), and fatigue cracks tend to start in areas of concentrated stress.  Additionally, if the fuselage has a non-circular cross-section, then the pressurisation stresses will want to deform it into one with a circular cross-section (as a circle has the greatest enclosed area of any closed shape with a given perimeter, and, thus, a cylindrical fuselage - i.e., one with a circular cross-section - has a greater cross-sectional area [and, thus, volume for containing pressurised air] than any fuselage with a non-circular cross-section), producing bending stresses in the fuselage - another way in which a non-circular-cross-section fuselage promotes fatigue damage.
However, a circular fuselage often isn't the best shape when you start wanting to put stuff in the aircraft, since the way the walls curve inwards as you go up and down can make it hard to put seats or cargo near the edges of the cabin.  Many pressurised aircraft, especially large pressurised aircraft, do have circular fuselages (as large-diameter fuselages have a lesser degree of curvature than small-diameter ones, causing this disadvantage to be less prominent), as seen (for instance) on the 777 and 787, but many others (especially smaller aircraft) use non-circular fuselages.  One way of doing this is to use a fuselage cross-section shaped like two overlapping circles (the Boeing 377, a.k.a. "Stratocruiser", is a spectacular example, but other aircraft, such as the DC-8 and DC-9, also use this method, although much less noticeably).  This produces a cross-section with a pronounced cusp at the intersection of the two circles; this would seem like it should create insane fatigue problems, but almost all of the stress concentration at the cusp is eliminated by stringing the floor between the two cusps to act as a tension brace, and the minimal amount that remains (due to the slight differences in mechanical properties of the hull and the floor) is easily dealt with by slightly thickening the skin around the cusp.
Another way is to make the fuselage taller than it is wide, decreasing the curvature of the cabin sidewalls while increasing the curvature at the very top and bottom of the cabin, and ending up with a fuselage that is... [drumroll] oval in cross-section!  Some aircraft (such as the A380) do something distinct but quite similar, where the upper fuselage is stretched vertically but the lower fuselage is not (in order to keep the floor of the cargo hold flatter), resulting in an egg-shaped fuselage cross-section:

(Image by EADS, via EADSpics [since taken down] at Flickr, via @aeroalias here at AvSE; the noncircularity of the A380's fuselage cross-section is especially prominent due to its having two passenger decks stacked one atop the other, requiring more vertical space than for a single-passenger-deck aircraft, but a great many pressurised single-deckers also have oval fuselages - just less-obviously-oval ones.)
Both the oval and the egg have the disadvantage of producing stress concentrations in the curvier parts of the fuselage, but this is easily dealt with by using thicker skin panels, and, potentially, more rivets, in these areas.  (The floor[s] tying the two sides of the fuselage together probably also help by acting as tension braces, just like for the cusped fuselage.)

1: If you want to be really pedantic, the aircraft doesn't pressurise as it ascends.  The pressure inside the aircraft actually decreases on ascent, up to a cabin altitude2 of 8,000 feet or so; however, the ambient pressure outside the aircraft decreases much more quickly, so the pressure differential between the interior and exterior of the aircraft does build up as the aircraft ascends.  This has exactly the same effect on the aircraft's structure as if you left the aircraft on the ground and pressurised it by pumping in more air - the structural stresses imposed on the aircraft don't care if the pressure differential is produced by increasing the pressure inside the aircraft or decreasing the pressure outside the aircraft.
2: The cabin altitude is the altitude at which the ambient atmospheric pressure (assuming a standard atmospheric-pressure profile) would be the same as what the pressure inside your aircraft is now.  For instance, if the pressure inside your aircraft's pressure cabin is the same as the pressure one would experience floating at 5,000 feet above mean sea level with no aircraft, your aircraft's cabin altitude is 5,000 feet.

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text:
How to artificially increase the Reynolds number in a wind tunnel?
I'm currently scaling down a model 64 times for a wind tunnel analysis, where I'm measuring drag force (for drag coefficient) and lift force (for lift coefficient). However, I read that scaling down 64 times means that wind velocity must be scaled up by 64 times to keep the Reynolds number constant. I read that using trip strips are a viable solution. How do I calculate the location, size, and number and strips of the slips required to increase the Reynolds number by 64 times so I can get accurate results?

Read about Dr. Max Munk and the variable density wind tunnel at the Langley research center, developed in the early 1920s.

Trip strips will approximate a higher Reynolds number in the sense that you get turbulent flow at a lower Reynolds number, but they will not increase the Reynolds number themselves. You will have different pressure and density gradients in the boundary layer, as though you were operating at a higher Reynolds number, but the number itself has no way of accounting for a trip.
The equation for the Reynolds number is $$\frac{\rho v d}{\mu}.$$ These are the only parameters you have to work with if you're going to be using the Reynolds number as your similarity parameter. If you absolutely have to use a wind tunnel, then increasing the model size or increasing the velocity are your only options (theoretically you could pressurize the wind tunnel to increase density if it were sealed, or you could change the temperature of the flow within the tunnel, but these have not been realistic options for any wind tunnel I've worked with). If you don't have to use a wind tunnel, a water tunnel is a viable alternative.
See An Assessment of the Usefulness of Water Tunnels for Aerodynamic Investigations for more details on water tunnels.

Cryogenic wind tunnels are a thing too: https://www.sciencedirect.com/science/article/abs/pii/0376042192900086

In the blow-down tunnels I've worked with, we were able to control the Mach number and increase Reynolds number at the same time. I assume that's done by increasing the density?

Hi, is it feasible to test at different velocities(and as a result, different Reynold numbers) and extrapolate the results? I know this will create error, but I hope the error will be smaller than just ignoring the Reynold number.

@itisyeetimetoday yes, you can do that, although you'll probably end up creating more error than you expect. The results will likely be good enough for a school report, but not for anything that would actually fly.

Reynolds Number is a relatively easy calculation to do:  Velocity x Chord Length/ Kinematic viscosity.  So, changing the fluid from air to water may be helpful.  I would also consider developing data points from varying degrees of scale, for example 1/128th, 1/64th, 1/32th for comparative purposes, as well as changing fluid velocity.
Also, a review of relevant performance data of anything similar to what you are testing, with or without  "trip strips",  may save you many hours in the laboratory researching what has already been done.
Finally, run your tests with a "control" of known performance to see if your methodology is proper for the "experimental" you are trying to test.

Thank you for your response! Do you have any link to research with trip strips and airfoils?

@itisyeetimetoday  also, because adding test strips, roughness, dimples etc is changing the airfoil, it is very important to do this first on the well known control (Clarke Y, Davis airfoil, NACA 0010, etc) and see if your polars match the higher Reynolds "real life" scale.  At that point, you move on to your experimentals.  Try to find a control that is as close as possible, and avoid the temptation of making anticipated results fit  the experiment.  Sometimes, for better or for worse, they don't.

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If a CDI needle is deflected to the right, why is the aircraft off track to the left?
Consider a CDI as shown below. If the CDI is set to FROM and the selected course is north, but the needle indicates three dots to the right (each dot signifying a 2 degree deviation from the selected course, i.e. 6 degrees in total), then why is the aircraft's radial at 354 degrees?
I associate a right movement of the needle with a "positive deviation", which would correspond to the aircraft's radial being at 006 degrees.

You're left of course, so the CDI is telling you to fly right so you get back on course.

The CDI indicates your desired course. The white circle in the center of the instrument represents your position. If the desired course is to the right of your position, you need to move to your right to rejoin your course.

Okay, it maybe is that simple. Thanks!

It is once you understand the instrument!  Excellent graphic by the way.


text:
Do I need to change cruising altitudes for really short legs?
Let's say I'm cruising on a magnetic course of 150, so I'm flying at 7,500 feet.  Then I need to fly for 6 miles on a magnetic course of 210, then back to 150.  Do I need to switch to 8,500 or 6,500 for the short 6 mile leg, or is it better to stay at 7,500?  And if I need to switch altitudes for the short leg and I'm getting flight following, do I need to request an altitude change for the short leg and then request to change it back when I resume a course of 150?

you should precise the jurisdiction you are interested in (what country, under what flight rules)

Related, if you're asking about the US. And I removed the IFR tag, since you've mentioned VFR altitudes in your question, and the whole thing would be very different under IFR anyway.

In the case presented in the question, I would not change altitude. Why not? I would most probably be cruising at or above 120 kts. So a 6 nm (I assume miles was referring to nm in the Q) leg would  take a whopping three minutes or less. To preoccupy myself with cruise descent, a minute or two of level flight and then cruise climb back to previous alt...
Nope.
I would much rather broadcast my position, my intention to fly a short leg at hdg x, altitude y and then continue with hdg z. Instead of being busy with alt changes (depending on acft a handful of check items), I would be maintaining extra vigilant lookout for this rude three minute violation of rules.
Then I would just wait for the call from the local aviation administration authority. Bet my bottom dollar I would not get one.
P.S. on a check flight I would change altitude. For obvious reasons.

As you are using the term flight following I'll assume you are in the US. Flight following is an advisory service, you tell them your intentions and they give you any traffic information you may have. If you are changing altitude or course you tell them, you do not ask permission because they cannot give it.
FAR 91.159 clearly states what altitudes you should be at using the semi-circular rule:

Except  while  holding  in  a  holding  pattern  of  2  minutes  or
less,  or  while  turning,  each  person  operating  an  air-craft
under VFR in level cruising flight more  than  3,000  feet  above  the
surface  shall maintain the appropriate altitude or  flight  level
prescribed  below, unless  otherwise authorized by ATC

So if you will be flying 3000ft or more above ground level you will be expected to fly the semi-circular rule, there are no exceptions made except those listed above. From a practical perspective you'll spend more time climbing and descending than at the other altitude so I think it's a fair question, the answer is to make the altitude change.

Did you mean to say "3,000ft or more above ground level"?

Yes I did, good call @Pondlife


text:
What does "pitch plus power equals performance" really mean?
It is often said in aviation circles that "pitch plus power equals performance".
A. What is it supposed to mean?
B. Is it always true?
C. If it isn't always true, why is it a useful concept nonetheless?

OK, I didn't downvote yesterday when you made this comment, but I downvoted it today.  I did this because sub-part C is asking for opinions, which is grounds for closure, and when I offered an opinion in my answer you rebuked me.

@MichaelHall-- seems to me that asking for an opinion about why a concept is useful to an aviator is different than offering someone an opinion that they ought not be overthinking or trying to discredit something.  But, will delete the "rebuke".  Seems you and I are doomed to be forever crosswise.

and I will remove my downvote when the system allows.  I agree too that certain educated opinions have a place here.  And to be completely honest, my DV was probably a wee bit retaliatory given my frustration with your comments.  However, I don't think the question is useful.  It is obvious that you have a tremendous amount of knowledge, but I am not sure what you are trying to accomplish here.  It is a very simple colloquial expression, nothing more.  It would be like asking what "aviate, navigate, communicate" means, then arguing exceptions to debunk it...

And yeah, we do seem to get crosswise here.  I'd love to meet you over a beer sometime, I bet we would clear the air and get along just fine!  We do both like to debate things...  ;)

A.  It simply means that the airplane will perform according to the combination of pitch and power control inputs that you make.
B.  Yes, why wouldn’t it be?  Aircraft are subject to basic laws of physics.  These laws are consistent.  Every time you pitch nose down and add power you will descend and accelerate.  Every time.
C.  N/A because it is always true, but it is just a saying.  If you find the concept useful to enhance your understanding or explain something, then use it.  If not, then don’t.  Aviation is full of such sayings to help pilots remember things, like “aviate, navigate, communicate”, “ARROW” etc.  Pick the ones you find helpful and don’t overthink or try to discredit the ones that aren’t useful to you.

"Yes, why wouldn’t it be?"-- I can think of a reason, but will save for later--

Yes, of course you can...  (are you thinking region of reverse command?)  Still, whatever scenario you detail out you would have gotten there as a result of previous pitch and power inputs.  But go ahead.

"Yes, why wouldn’t it be?" Pretty sure that the mechanics of supersonic flight are different than those of subsonic flight.

@nick012000, true, but those supersonice mechanics also follow predictable laws, that are affected by... pitch and power.  Right?

@MichaelHall-- re recent edit-- I see nothing wrong w/ trying to discredit the idea that an excessive (or even just an increased) pitch attitude does not always result in more performance.

PS the answer begs the question, does "pitch" in the saying refer to pitch pressure on control stick or yoke, (or position thereof), or aircraft pitch attitude?

@quiet flyer, neither the saying nor my answer claims that increased pitch attitude results in "more" performance.  (whatever that means...)  The point is that changing either pitch or power will result in a corresponding change in the aircraft's performance.  It will always change, maybe for the better, maybe for the worse.  But again, it is just a saying; it isn't intended as an engineering formula.  Sub-part C of your question asked for a subjective assessment of the saying's usefulness.  I felt that my answer was appropriate to what you were asking.

I would add that the reason that this exists is to remind students that any change in either pitch or power will change performance unless you also change the other to compensate, or that if you do want to change performance, there are two ways to do so.


text:
How should a private pilot renew their part 107 certificate?
I got a Part 107 (Commercial Drone) Certificate by passing the test more than two years ago, so it's expired now. I just became a private pilot, and I know that private pilots can get a Part 107 Certificate if they take a few online courses from the FAA.
But since I have the Part 107 from passing a test and now want to use my private pilot certificate to renew my expired Part 107 certificate, how do I do this?
It seems a little convoluted because it's a renewal, not an original certificate.

As a holder of an FAA private pilot certificate, you can take a free course to “renew” a Part 107 certificate. You will first have to create and register an account on the FAA Safety Team website. You should do this anyway to earn WINGS credit toward your next flight review.
The site states..

The Part 107 Small Unmanned Aircraft Systems (UAS) Recurrent course describes the operational requirements to continue to operate small UAS in the National Airspace System (NAS) under Title 14 of the Code of Federal Regulations (14 CFR) part 107, small Unmanned Aircraft Systems. ***Note: This course may be taken by remote pilots who qualify for relief under Special Federal Aviation Regulation (SFAR) No. 118 to satisfy the aeronautical knowledge recency requirements of 14 CFR 107.65(a) or (b) for a period of six calendar months. FOR PART 61 PILOT CERTIFICATE HOLDERS WITH A CURRENT FLIGHT REVIEW (IN ACCORDANCE WITH 14 CFR PART 61.56), SUCCESSFUL COMPLETION OF THIS ONLINE COURSE SATISFIES THE RECURRENT TRAINING REQUIREMENT TO REMAIN CURRENT AS A PART 107 REMOTE PILOT WITH A SMALL UAS RATING. All other interested individuals may complete this online course as a self-study resource.

A Part 107 certificate does not have an expiration date. You lose the privileges associated with it if you do not renew your currency by taking a refresher course.
The FAR/AIM states...

§107.65 Aeronautical knowledge recency.
  A person may not operate a small unmanned aircraft system unless that person has completed one of the following, within the previous 24 calendar months:
(a) Passed an initial aeronautical knowledge test covering the areas of knowledge specified in §107.73(a);
(b) Passed a recurrent aeronautical knowledge test covering the areas of knowledge specified in §107.73(b); or
(c) If a person holds a pilot certificate (other than a student pilot certificate) issued under part 61 of this chapter and meets the flight review requirements specified in §§61.56, passed either an initial or recurrent training course covering the areas of knowledge specified in §107.74(a) or (b) in a manner acceptable to the Administrator.

Thanks!  I went to the website and finished it.

Wow! One of those rare Aviation questions with a pretty cut 'n dry regulatory answer.

@FreeMan - sshhhhh... Don’t tell the FAA. They’ll change the regs.

@SurfandSky - Don’t forget to rack up those WINGS credits. The UAS course counts as one credit. Earning a WINGS phase by getting enough credits counts as a 24 calendar month Flight Review.

Because you are now a private pilot, your Part 107 certificate automatically renews when you take your Flight Review every two years. Passing your private pilot checkride counts as a Flight Review, so you are good until the end of the month two years from your checkride date.

§107.65   Aeronautical knowledge recency. (c) If a person holds a
  pilot certificate (other than a student pilot certificate) issued under part 61 of this chapter and meets the flight review requirements
  specified in §§61.56, passed either an initial or recurrent training
  course covering the areas of knowledge specified in §107.74(a) or (b)
  in a manner acceptable to the Administrator.

You can renew your certificate by passing the test but it is not necessary. In my case I took the initial training and got my certificate in October of 2017. I got a flight review in December of 2017 which renewed if for two years. I passed my IFR checkride in May of 2019, which renewed if for another two years.
Because I had some time, I took the course again in April so I am good until the end of April 2022.


text:
How should I make a downwind departure from a towered airport?
I'll be departing from a towered (Class D) airport, and I need to make a left downwind departure and turn right off the downwind leg to exit the pattern.
I've done this with a CFI, and I've also made left crosswind departures, and each time I climbed at full power above the traffic pattern altitude (TPA) while still on the downwind/crosswind leg, and I exited the downwind/crosswind leg whenever I felt like it.  I never really thought about whether I needed to stay at TPA all the way to the end of the leg, or whether I needed to complete the leg before exiting.
Do I need to stay at TPA while in the pattern, or can I climb above TPA since I have told the tower I plan to depart?  And when can I leave the pattern?

What does your departure clearance say?

All they've said in the past is, "Clear for takeoff, left turn approved," or "I'll call your left turn."  After that they didn't say anything until, at about 3 miles from the airport, "frequency change approved."  I have usually climbed to 2500 feet, most of it in the pattern, and the tower has never corrected me.

When ATC is vague, like "left turnout approved", it's because they don't really care what you do (within reason). They have zero problems being specific when they do care.

Typically, you have to think about each phase of flight in three dimensions (sometimes four if you consider time and timing of maneuvers). To be “in the pattern”, you have to be within the patterns lateral boundaries (not the right terminology) and at the proper altitude.
I consider myself to be in the pattern within a mile of the runway and below 1500 feet AGL. At this distance, I can still affect a power-off landing if my engine quits. Although the airport might designate a specific direction for the pattern, I consider either side of the runway as being in the pattern. This is just in case ATC gives instructions to fly counter to the typical pattern, or another pilot does not know the designated direction.
When exiting the pattern, you follow ATC instructions. They even have the prerogative to have you cross over the airfield abeam midfield when you are on the downwind. In the absence of ATC instructions, your best practice is to do one of three things. They are...

Continue straight out on the same course as either the departure leg or the upwind leg. Sidestepping to the upwind leg should get you out of the way of traffic landing on the opposite runway (same pavement). Once you are two or more miles away or above 1500 feet AGL, you can turn to your planned heading. If your desired heading will take you back over the airfield, try to be above 2000 feet AGL.
Once you are past he departure end of the runway, turn in the general direction of the traffic pattern. Keep your turn between zero and ninety degrees while continuing to climb out. Once you are two or more miles away or above 1500 feet AGL, you can turn to your planned heading. If your desired heading will take you back over the airfield, try to be above 2000 feet AGL.
Remain within the lateral track of the airfield during your entire climb to at least 2000 feet AGL. Once you are two or more miles away or above 1500 feet AGL, you can turn to your planned heading. If your desired heading will take you back over the airfield, try to be above 2000 feet AGL.


text:
Does a METAR report variable wind direction in a clockwise direction?
Does the convention for reporting variable wind direction always use a clockwise (nautical) sense?
For example, if the wind varies between 340 degrees and 10 degrees, assuming a clockwise sense the METAR item would be 340V010, but is 010V340 also correct?

I think it is always reported clockwise. A way to check is to remember that the mean wind direction should always be contained in the variance range.

Very related: https://aviation.stackexchange.com/questions/38528/what-are-the-criteria-for-variable-in-metar-reports Note especially that there are different ways of reporting less than 180 degrees of variation and more than 180 degrees of variation. So in any case, when you have xxxVyyy, it will always be the "shortest" way between those two values

I was just wondering this very thing earlier this afternoon.  What a coincidence.

According to meteocentre.com variable wind directions are encoded in clockwise order:

This group reports variations in wind direction. It is only included if during the 10 minute period preceding the observation the direction varies by 60 degrees or more, and the mean speed exceeds 3 knots. The two extreme directions are encoded in clockwise order.

(http://meteocentre.com/doc/metar.html)

I added a quote from that page. Link only answers are discouraged since the link could become invalid.


text:
Gliding: why pulling the stick back in a spiral dive would tighten the turn?
I have recently done my spiral dive recovery lesson in a glider ASK21.
The instructor taught me to level the wings first, then ease out of the dive by pulling the stick back. He said that pulling the stick back would only tighten the spiral and not help with reducing the speed.
Why is that? Should the nose not pitch up and reduce the speed?

Also, once you've rolled wings level, don't pull the stick hard and suddenly, unless ground impact is imminent. Doing so may exceed the structural limit of the aircraft. Pull it smoothly.

The effects of rudder and elevator get mixed when the aircraft flies at a roll angle. See it this way: When you pull the elevator at a roll angle of 60°, it will mostly (86.6%) work like a rudder would for a level airplane.
Why those 86.6%? When looking at the aircraft in an earth-fixed reference system, the additional tail force from an elevator deflection will produce a side load component proportional to the sine of the roll angle (which is 86.6% at 60°). The vertical component which would help to get the nose up is only 50% at a roll angle of 60° because it is proportional to the cosine of the roll angle.
Coordinated flight at higher roll angles is almost like flying a loop sideways. You will only lift your glider's nose in the reference system of the glider and tighten the loop. The reference system that counts more here is the one in which gravity acts, and you should lift the glider's nose up in this system.
Not knowing this subtlety ended the life of several early aviators until it was found out in 1912 that the rudder is what lifts the nose in a spiral dive. Of course, it is even more efficient to first roll wings level and make the elevator work properly again.
The horizontal-loop thing works in reverse, too: Rüdiger Kunz, the designer of the Standard Austria, was always fond of telling the story that happened on occasion of the first flight: At some point, the pilot started to fly loops. After the third, he asked Herr Kunz over the radio: "Notice anything?" - "Yes, you're climbing" was his answer. Thereupon the pilot replied: "That's how you can circle in thermals, too!"

Rudder lifts the nose in a spiral dive, but it does not do much to arrest the dive, just makes the plane descend sideways, doesn't it? You still need to reduce the bank angle to get the vertical lift to arrest the dive.

@JanHudec Yes, absolutely. I only mention it to show that it influences the attitude in banked flight like the elevator does in straight flight.

In a steep spiral with a steep roll attitude, that is true as most of the lift vector is directed into a horizontal component.  Therefore aft stick pressure is simply going to force the aircraft into a tighter turn.  In addition this is going to impose much higher structural loads at high air speeds which may be beyond the design limits of the glider and put you at risk of a structural failure.  Your best bet from a steep spiral is to roll wings level, then pull out of the dive.

The other posts answer the question, but I think they fail to make an important point, or at least they fail to emphasize it. You are practicing the Spiral Dive Recovery, which is a "recovery" procedure. You are trying to extricate yourself from something like an unusual attitude. You are attempting to recover the aircraft, and not trying to stay in the turn!
If you are recovering from a spiral dive, then you level your wings first so that when you pull back on the stick all the lift generated is towards getting you out of the dive. This is the "recovery" of the exercise. This is solely about stopping your descent.
If you remain in the turn while pulling back on the stick then some of the lift will go into tightening the turn, instead of pulling out of the dive.
It might be possible that your intention is to be in a safe spiral dive, and in that case it might be appropriate to tighten the turn. For example, you might want to get the nose around quicker. This would not be a typical recovery procedure though.
I was doing a popup delivery in the single seat, light-attack jet A7-E Corsair when I successfully "recovered" from a turn in a steep dive. At 100 feet AGL, 750 MPH, with the target 3 miles away the pilot pulls the nose up to between 15-30 degrees to reach an apex in the climb of approximately 3,000 feet. At the apex the aircraft is rolled on its back and the target identified, pulling the nose onto it while inverted. In a 7-15 degree dive the run is made and bombs released with the egress fast and low. This is a very dynamic maneuver close to the ground, with lots of tasks to complete in a short period of time.
I found myself in the dive while still in a hard turn trying to get my nose on the target to release my bombs. The HUD indicated a 15 degree dive, and a safety article I read months earlier flashed through my head. Thank you Grandpa Pettibone! "If you find yourself in a 15 degree dive in a popup maneuver level your wings immediately and pull up." If I hadn't leveled my wings, and tried to stay in the turn while recovering I wouldn't be writing this today. As I came over the cleared target area, pulling in buffet, and finally had the flight path directed above the ground, I was looking up at the tree tops that surrounded it. This is a successful recovery procedure.

yikes!  sounds scary.

It may help you to understand the situation if you consider this-- imagine that you trimmed the glider for a moderately fast glide-- like perhaps 60 or 70 knots.  Now without exerting any forward or aft pressure on the stick, slowly roll the glider into a steep bank-- perhaps 45 or 50 degrees.  You'll find the airspeed rapidly increases as the glider enters a spiral dive.  This is partly due to the fact that for any given angle-of-attack, the steady-state airspeed is proportional to the square root of the load factor, and banking increases the load factor.  This is also partly due to the fact that an aircraft-- especially a relatively slow-flying aircraft like a glider-- tends to trim to a lower angle-of-attack in turning flight than in linear flight, due to aerodynamic effects generated by the curvature of the flight path.
Once the glider has entered the spiral dive, you'll find that simply rolling the wings back to level is sufficient to make the flight path start curving up out of the dive toward the trajectory associated with the original trim speed-- even if you exert no aft pressure on the control stick at all.  The reason for this is that as long as the glider retains some of the excess speed associated with the spiral dive, the wing is generating too much lift to allow the flight path to simply continue in a straight line on a diving trajectory.
Conversely, if you've ever practiced taking your hands completely off the control stick and controlling the aircraft via rudder inputs only, so that you are not making any pitch inputs at all, you've noticed that the rudder has a roll effect, and you've also noticed that the nose tends to rise as you roll towards wings-level, and tends to descend as you roll toward a steeper bank angle.
So it's clear that simply decreasing the bank angle, without pulling the stick aft at all, is sufficient to allow the aircraft to eventually recover from a spiral dive.  On the other hand, as other answers have noted, if the bank angle gets steep enough, then pulling the stick aft without decreasing the bank angle will not bring the nose up toward the horizon.

Potential future ASE question-- something along the lines of-- how to compute the exact combination of bank angle and trimmed airspeed at which moving the stick aft no longer brings the nose up relative to the horizon--

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text:
Do autopilots have an 'activate' switch/button, in addition to 'on' and 'off'?
Say cruising at FL310 and on a 270 heading with autopilot on. If pilot decides to descend to say, FL180 on a 180 heading, is simply changing the altitude and heading numbers on the autopilot control panel enough for the autopilot to get going with the new commands, or after changing the altitude and heading request, there is some sort of button that commands the autopilot to execute the new commands? And if so, where is that switch (or button) and what is it called?

I think "commit" is a better word than "activate" for what you describe

It is complicated (-;
First thing first, autopilot systems come with a variety of forms and complexity. The autopilot on a Cessna 172 or Piper Cherokee is going to be very different than the one on a Airbus or Boeing. Different manufacturer will also design their autopilot interface differently; while there are certainly similarities, there is no set standard in the aviation industry for autopilot interface and behavior.

(...) is simply changing the altitude and heading numbers, or (...)
  there is some sort of button that commands the autopilot to execute
  the new commands?

Both.

Here I will discuss using the Boeing 777 autopilot, which I am familiar with. On the autopilot panel, there is a heading window, which displays a 3-digit number. Directly below the window is a knob, turning the knob counterclockwise will decrease the heading, while turning clockwise will increase it. The knob can also be pushed.

The heading section of the Model Control Panel on a Boeing 777. The knob is a 5-in-1 control: the outer ring can be rotated, the knob can be rotated, and the center of the knob is a push button.
If the autopilot is in "HDL SEL" mode, it will fly the heading specified in the window. In this mode, if the pilot rotates the knob to adjust the heading, the new heading will take effect immediately. However, if it is in "HDL HOLD" mode, turning the knob will adjust the number, but it will have no effect - the plane will hold the current heading. Pushing the knob will change the mode from "HDL HOLD" to "HDL SEL", and the plane will then turn towards the selected heading.
A similar logic exists when climbing using the "VNAV" mode. Let's say the plane is initially cleared to 5000 feet after takeoff. The pilot set the altitude window to 5000 prior to the takeoff roll. Once autopilot is engaged, it will climb to 5000 feet, after which it will hold that altitude. At any point, the altitude knob can be rotated to set a new altitude, say 7000 feet, however it will not take effect - the plane will still climb to 5000 feet, then stop the climb there. To climb to a higher altitude, the pilots have to push the knob, after which the plane will initiate a new climb from 5000 feet to 7000 feet. This is because ATC often clear planes to "step climb", i.e. climbing then holding at certain altitudes until reaching the cruise altitude. The autopilot function is designed around that.

where is that switch (or button)?

It depends on the model. Other manufacturers call them differently, but the logic is similar. Also, advanced autopilots have a lot of functions; the ones I discussed are just selected examples about heading and altitude selections. Pilots can also "arm" an autopilot mode, i.e. mark it so that it will become engaged when certain conditions meet. The specifics of that are too long to describe in this post.
Like I said, it gets complicated.

"At any point, the altitude knob can be rotated to set a new altitude" Does this "any point" include during the initial climb? Say, pilot initiates a climb to 5000 ft, and before reaching 5000 ft, increases the target altitude to 7000 ft. In such a scenario, does the plane still level off at 5000 ft or does it continue climbing to 7000 ft without pausing at 5000 ft?

@MichaelKjörling it depends on when VNAV is engaged. If the altitude is changed before VNAV is active, the plane will fly straight to 7000 ft. If it is changed after VNAV is active, the plane will level at 5000 ft. If VNAV is engaged during the initial climb (which is usually the case), then the answer to your question is "it will level at 5000 ft".

No wonder so many incident reports on AvHerald involve autopilots in a mode other than what the pilot thought they were in.

It varies between AFCS units, but in general most have different steering and vertical selection modes.  Steering modes in general allow the AFCS to track either a desired heading or a course generated by terrestrial or GPS navaids.  Vertical selection modes in general allow the pilot to enter an desired altitude and various types of climb methods ie constant vertical speeds, constant airspeed climbs, vertical descent planning, etc.
In the scenario you just mentioned a pilot might set his AFCS to HDG mode, then select 180 on your heading bug knob.  ALT mode would the be selected, dial in 18000 on your altitude bug, then select V/S mode and select -1000 to set a descent rate.  The autopilot can then fly the aircraft on a heading of 180°, and descend the aircraft from FL310 to FL180 at 1000 feet/min.

Heading change is much less critical than climb or descent. So most of the autopilots will start turn immidiatly. Climb or descent is more complex. You can run out speed and stall in climb, over speed in descent or hit the ground. Also all turnings are done with preset bank. For climb or descent autopilot has to know how to do that. Keep vertical speed or forward speed or specific angle. So more buttons to push. Also this also helps with additional monitoring of the selected altitude. Pilots has to monitor this more actively because you can soon end at the wrong speed. In turn you can loose several knots but it most cases no any problems at all. Otherwise if you set wrong vertical speed or forget to add throttle in climb you can stall very soon.

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text:
FADEC or EEC for PT6-42A...is it feasible?
In a response to a You-tube clip showcasing Piper's M600 single turbo prop, a viewer dismissed it as an inferior engine compared to a GE (probably an H-80 series) due to lack of FADEC or Electronic Engine Control (ECC) which GE engine has but lacking in PT-6.
Since controlling the PT-6 on the above aircraft does not seem to require a big workload from the pilot, I am wondering is there any necessity to equip this engine with FADEC, and whether the cost/benefit ratio is justifiable?

AFAIK FADEC is just a throttle limiter to an engine. Its a computer that sees all inputs from the engine sensors and limits the thrust accordingly.

@MarceloPacheco: FADEC controls fuel flow, but also the engine components themselves, to optimize flows, pressures and temperatures, and prevent compressor stall, using blade/vanes adjustments, valves and tip clearance mechanisms.

It is quite feasible and available on other PT-6 family engines. The PT-6C engine is available with FADEC but appears to be more for rotorcraft. That being said its fundamentally a similar engine and the systems could be migrated to the common PT-6A.
The question of:

I am wondering is there any necessity to equip this engine with FADEC

This is somewhat of an opinion based question depending on what you personally feel is necessary. FADEC allows a pilot to run an engine at optimal performance all the time without needing to babysit the various engine parameters and settings. Some see this as a great benefit (taking something off your plate in a demanding airplane) while the more classically minded prefer to have finer control and operate their engines in various ways that may be considered less than optimal but appropriate for the mission.
The cost of FADEC is putting the engine control in the hands of a computer, which many are slowly becoming comfortable with. One thing to consider on smaller planes like the M600 is backup power systems. Large planes have the luxury of things like an APU and  a RAT as well as lots of alternators and battery banks to mitigate power failures across 4 discrete power sources. The M600 has only its alternator and batteries as a backup so in the event of a power loss you have less to fall back on and may lose the engine.

whether the cost/benefit ratio is justifiable

Without knowing P&W's financials its hard to say. They are clearly selling lots of PT-6's and many might say theres no reason to change something that works. Since they clearly have a FADEC system for the PT-6C I would imagine a great deal of the work has been done and the system could be migrated to the PT-6A at least in part but you would need someone from PW to confirm that assumption.

Just a bit of a history note the PT-6A is a fairly old engine and has been around since the early 70's a time long before FADEC was small enough for something like the M600. On the same note the PA-46 first flew in '79 a bit before FADEC was viable on a small scale. There is some reality to keeping up a certified config once its certified.


text:
Has any Cessna Denali ever flown yet...?
With all the articles and hypes around the new Cessna Denali with its GE catalyst turbo-prop engine, I am wondering has any prototype of this plane made it into the air yet?
I understand that the performance figures can be partly calculated but am wondering how they can be so specific about its speed, range, load, and fuel consumption? Thank you.

According to Flying Magazine's September 2018 profile of the Denali:

The Denali’s first flight is expected early next year, with an entry
  into service during the first half of 2020.

As for the performance figures you mentioned, the same article says:

The Denali will weigh less than 12,500 pounds to prevent the need for
  a type rating, but at the moment, Cessna hasn’t released a gross
  weight number, nor any performance figures. Those won’t be made public
  until after the Denali’s first flight next year.

Based on the same Flying article, its 285 KT cruise is the same speed of a Pilatus PC-12, or slightly faster than a Piper M-600, and 50 Knots slower than a TBM-930. It's range is lower than PC-12 and TBM, The useful load figure is not determined yet but the number of seats is given is given 8-11...! Not sure how many can be filled up.

It’s currently under development.  Rollout hasn’t even happened yet, but is expected to occur late in 2018 or early 2019.
UPDATE:  The Denali along with the SkyCourier have been delayed into 2020 due to delays in Citation Longitude certification.  As that program wraps up, Textron can shift more manpower over to the these programs and finish up.

Latest news says first flight is planned in 2020, due to engine testing delays. https://www.ainonline.com/aviation-news/business-aviation/2019-10-21/cessna-denali-first-flight-delayed-2020

With five development engines assembled and more than 1,600 hours of combined operation between engine test hours, GE Aviation’s new Catalyst turboprop engine is progressing toward a flying testbed for the launch application, the Textron Aviation Denali. However, the engine maker won’t deliver the first Denali flight-test engine to Textron Aviation (Booth C9343, Static SD503 and SD503A) until sometime in 2020, GE officials confirmed on the eve of NBAA-BACE.


text:
What is this dome used for?
I have seen this dome on the top of some 737-800 airplanes and am curious to know  what is it for. Is the a communication antenna for the satellite connection and in-flight internet that some airlines are providing?

That fairing covers an antenna for a satellite-based Wi-Fi system.


text:
What kind of low pressure causes abnormal RPM variations?
I was wondering what kind of low pressure indication causes abnormal variations in the RPM of a Lockheed L188 Electra. I was told one of the engines was presenting low pressure readings at certain rotations. Would that be low engine oil pressure? I have read the Electra manual and only saw indication of low pressure for either hydraulics or engine oil. The call of low pressure was originally made by the FE, which makes me think it should be something that would show somewhere in the flight station.
Thanks
In this link the only relevant low pressure indications I found were of engine oil and of hydraulics.
https://publicapps.caa.co.uk/docs/33/SRG_ACP_L188_REV2_ALL.PDF           .
Presumably everything should be there, although I was subsequently told that it could also refer to manifold pressure.
Here, https://www.spruemaster.com/blog/wp-content/gallery/manual/Lockheed%20L-188%20Electra%20-%20%20Electra%20Flight%20Control%20S%20ystem%20Part%201.pdf              ,
on page 30, fig.24, there is a picture of the flight station . I had originally only seen the four lights indicating low engine oil pressure (top left corner, listed as part of the "Ess Ac Inst Bus"), but upon closer examination, I found other things related to pressure as well. Perhaps I was biased because the first documents I read only mentioned hydraulics and engine oil.
So I guess my question should be: what kind of low pressure  is the cause of (or is caused by - the Captain was not very clear) abnormal RPM readings.
Thanks a lot
Ps: I tried to upload the flight station image here, but didn't manage. It sad it was too big. My apologies.

Could you clarify your question? 1/ "low pressure indication causes abnormal variations in the RPM" and 2/"one of the engines was presenting low pressure readings at certain rotations". In one case low pressure is the cause of RPM variation, in the other case specific RPM are the cause of low pressure. What is the actual chain of events you want to be explained?

What do you mean by "kind of low pressure"? You may specify if you what to discriminate fuild circuit (hydraulic, oil, fuel,...) or the causes of this low pressure inside on kind of fluid circuit.

Leave open but we will need a little more clarification from the OP before this can be accurately addressed.

@ mins - thank you for pointing that out. I actually only transcribed what the Captain had said , so it never crossed my mind to evaluate whether they made sense. But you are right, they did sound contradictory. As it was the FE that called the low pressure first , I think DeltaLima edited it correctly, leaving the first part of the question in and removing the second. Thanks

@ Manu H - I added some more information to the question. I do not know what kind of low pressure we are talking about, which is why I came here for help. I realise than when talking about an aircraft there are loads of options and I did try my best to find out to which of those the Captain was referring to, but I have failed nonetheless. At this point I am almost sure that we are referring to low engine oil pressure, but I needed to be sure if that would cause abnormal RPM readings (or be caused by). Thanks

@ Carlo Felicione - I added some information to the question. I hope that helps. Thanks

Ok, so I found out it was oil-related, as the aircraft mechanic had to change the oil filter. I am still unclear as to what caused what (low oil pressure caused abnormal RPM or the other way around). Should I edit this question to ask only this much now? It seems my attempt to make the question clearer was unsuccessful. Thanks


text:
Why is it that T-tails want to climb like on a PA-44? It seems like it always wants to climb
I'm having a little difficulty understanding the aerodynamics of a t-tail and how it affects climb.

Can you elaborate on what is it that you find unusual or don't understand? At first glance that sounds like the aircraft is pitching up because it is not trimmed.

Because of the location of the horizontal stabilizer, it isn't as affected by the power setting. Thus, it's likely that you are trimming to compensate for power reductions when you don't need to. I would make sure you trim well, and ensure you are trimming based on what the airplane needs rather than what you would put in on a Cessna.

It's important to remember that airplanes trim to a speed.  If the trim control and tab is at position X, the airplane will seek a speed of Y, pitching up or down as required until it's at its trim speed.  The trim control is effectively a speed setting dial, in terms of what the airplane wants to do if left on its own.  If the airplane wants to climb, it's because it has surplus thrust at its trim speed, T tail or no.  If you are trimmed at 120 kt in the Seminole and it wants to climb, it means you have too much power for level flight at 120 kt.  If you don't want it to climb, either reduce power or trim to an airspeed that gives level flight at that power setting.
Normally located horizontal tails in tractor airplanes are subjected to trim speed changes when thrust is changed, because the thrust changes modify tail down force, the tail being in the propellers wash.  Adding power increases the downforce and reduces the airplane's trim speed.  If you're trimmed at 90 kt in a 172 at a certain power setting and add more power, the airplane will pitch up as it seeks to maintain its 90 kt trim speed.  But the stronger slipstream from the prop "fools" the tail into thinking its still too fast even when at 90kt, and will seek a slightly slower speed, say 87 kt.  Opposite happens when reducing power.
A T tail, being up mostly out of the propeller stream, is much less affected by power changes, only to the extent that there are pitching moments due to the prop's thrust line; in this they they are more like a jet with tail mounted engines (add thrust without touching the controls and it pitches down slightly due to the thrust increase, accelerates, than starts to pitch up and go about seeking its trim speed while climbing).
So when you add power to climb with a T tail, there isn't the immediate up pitching tendency from the propeller wash "blowing harder" on the tail; there is only the pitching tendency from the increased airspeed itself as the airplane initially accelerates from the added thrust, and the increased free stream airspeed "blows harder" on the tail.  So overall there is a much more mild response to power changes and the airplane has a stronger tendency to accelerate a bit before pitching up.
In a normal tail you add throttle and it pitches up almost right away, but once you've stabilized in the climb, you may find your trimmed speed is a bit lower than before and you have to add a bit of nose down trim to keep the same trim speed as when you started.
With a T tail you add throttle and initially there is little pitch change until the airplane accelerates and then starts to pitch up.  You can help it along with a bit of up elevator minimize the initial speed overshoot and hunt that results. However, when it's all settled down in the climb and everything's back in equilibrium, you should still be pretty much as the same trim speed as you started.  If the trim speed changed it's only to the extent that the engine's thrust line increased or decreased the thrust line's pitching tendency, if there is one.
The other effects of T tails are related to its location that takes it in and out of the stronger downwash flow coming from the wings.  When the airplane is pitched up on takeoff for example, the tail starts off high enough to be minimally affected by the wing's downwash, but then as the tail comes down at rotation, it descends into the downwash and suddenly sees more negative angle-of-attack and therefore more downforce than before.  This results in the phenomenon common on T tails where you have to pull fairly hard to lift the nose but then relax some of the pull as soon as the airplane lifts off to keep from overpitching.


text:
How does an engine work when an airplane has $v=0$ on the ground?
I mean, for a turbofan:
$$ T= \dot m_{air,h} (1+f) v_{e,h}+ \dot m_{air,c} v_{e,c}- (\dot m_{air,h}+ \dot m_{air,c} ) v_0+ (P_{e,h}-P_{amb} ) A_{e,h}+ (P_{e,c}-P_{amb} ) A_{e,c} $$
but
$$ \dot m_{air}=\rho Av_0 $$
do I have to impose  $\dot m_{air}$?
in this case how the thrust expression change (in particular the terms with $v_0$)?

In your second equation, $v_0$ should be the speed of the air moving through the area $A$, not the speed of the aircraft, right?

It works the same way as it does in the air.  The only difference is that there is no ram air at the intake, the compressor has to suck air in.

@Bianfable Yes, I think it should.
But in my propulsion course we often approximate $v_{inlet}=v_{aircraft}$. I think that my doubt come from this!

The question you probably should ask when someone says something like "but $\dot m_{air}=\rho Av_0$" is why does that hold? You can turn this question around by asking yourself: what happens if the aircraft is stationary on the ground, pointed directly into the wind, with a wind speed of (say) 30 kt? Now consider the opposite case: what happens if there is no wind (perfectly calm air), but the aircraft is somehow being propelled forward at a speed of 30 kt with no friction losses against the ground? From the aircraft's perspective, what is the difference between the two cases?

As a practical example, you might note that somewhat modified jet engines are widely used for electric power generation: https://en.wikipedia.org/wiki/Gas_turbine#Industrial_gas_turbines_for_power_generation

@aCvn That makes perfect sense! Now my problem is understading in the thrust formula if the $ v_0 $ is the aircraft speed or the speed of the air at the intake. Can you help me with this?

@wilove Bianfable's initial comment seems to apply to your recent followup-question comment. If you need more clarification than that, I'd encourage you to ask it as a separate question. In general, comments are for suggesting improvements or requesting clarification to the post they are attached to; broadly speaking, comments are not for somewhat-related followup questions that you realize that you want answered based on the answers and/or comments you get to an existing question.

To start the engine, the fan blades have to be spun up. This is typically handled by either blowing air through them from some outside source, and/or by using an APU to generate power to drive the shaft they're connected to.
Once the engine is running, it sucks in enough air to keep going on its own.

And the airflow has velocity $v_0$ which differs from zero when the aircraft is stationary.

Therefore, should I impose $\dot m_{air}$ and calculate $v_0$ knowing the intake geometry? In this case I have one more question: $\dot m_{air}$ is fixed with altitude variation or not (or at least is it a reasonable approximation)?

$v_0$ is the airflow speed through the engine, not the airspeed. As per @Bianfable’s comment.
How the engine works at standstill: the compressor sucks air into the inlet, it initiates the flow through the engine. Axial compressor blades similar to a propeller, centrifugal compressors by slinging air out towards the compressor outlet.
Maximum thrust at standstill should be a given for the engine under consideration. At standstill, if the exhaust is choked, the mass flow follows from:

Thrust.
Speed of sound at the exhaust gas temperature.
Exhaust pressure and area.
Bypass ratio.

With the mass flow given, you can compute $v_0$


text:
Is specifically indicating "uncontrolled airfield, student handling radios" by writing "uncontrolled" in a student's log book necessary?
I'm a student pilot with 52 flight hours.  I've had multiple lessons at the same uncontrolled airfield handling the communications on each leg while doing touch and goes.  The last lesson my instructor wrote "uncontrolled" in my log book.  I spoke with the chief flight instructor she said that it was to indicate that I was flying in an uncontrolled airfield and handling all the radios.  Is it necessary to reflect radio communications for the private pilot exam with the DPE?
As I indicated above all my flight training for touch and goes (except one) has been at one uncontrolled airfield.  After the first lesson on calling postions in the pattern I've handled all radio communications.  Is writing "uncontrolled" necessary for logging progress?
Thank you.

Could you add a tag to indicate which jurisdiction you are asking about (e.g. faa-regulations for the US)?

Hi ubah, and welcome to Aviation Stack Exchange. I agree with Bianfable above that this question needs to specify a jurisdiction (though your mention of DPE makes me think you may be looking for answers for the US; either way, it's better to spell it out). I also edited the title of your question to try to better summarize what you are asking. If you feel my edit changed your intent in any way, by all means feel free to [Edit] further.

If you haven't spent any time at a controlled field, I'd ask your instructor to do your next set of T&G's at a controlled field. Try to get some variety, Class C and D. Getting into the controlled airspace and into the field can be intimidating if you've never done it before. Don't do it for the first time with your DPE.

I think the concept of "it's your (log)book, write in it whatever you want to" sort of applies.  Things that NEED to be recorded to prove currency & requirements accomplished, need to be there.  Stuff you WANT recorded, as a memory jogger or to reminisce later, can be there.  Extraneous stuff isn't really a harm, but if it doesn't reflect requirements met, it doesn't have to be there. Noting experience at both controlled + uncontrolled airports could be nice to have, tho looking up the airport can do that too (unless it closes or changes status).

@RalphJ Even if the airport closes or changes status, surely historical records could be referenced to determine its status at the time? After all, some airports switch between controlled and uncontrolled based on time of day or day of week, so even absent that, it's not as simple as being one or the other...

You need to specify that the requirements of training are met.
For a private pilot under the FAA system, you need to have completed three solo landings at a controlled airport.  Otherwise, radio communication is a required line-item for training.  You should always log the airport of departure and arrival as well as the date.  If someone wants to know whether it was controlled or uncontrolled, they could look up the airport and see if it had a tower on that date, but they shouldn't need to since the required solo with an operating control tower should be specified in your training remarks.
Any examiner in the area would likely know whether any given airport is controlled or not simply from memory, being familiar with the area you're in. The examiner must check to make sure you meet the minimum requirements for the certificate or rating.
Beyond the three landings with a tower and the required standard communications training, there is no need to specify controlled vs. uncontrolled airport operations.

Thank you for all the help.  I updated for faa-regulations.  The flight school is within class c airspace with a control tower.  I do the t/g's at an uncontrolled airport.  This is just the first time he wrote uncontrolled in my log book and I was advised that it indicated uncontrolled airport and I was doing all the communications in the pattern.

@ubah Yes, you may write anything you would like to.  You don't need to specify controlled or uncontrolled other than to meet the requirements of 14 CFR 61.109(a)(5)(iii).


text:
Will there be dynamic or variable separation minima in future?
In the future, is it possible to apply in the same airspace different separations between pairs of aircraft? Depending on the relative speed, navigation capacity of the aircraft, intersection geometry, etc.
What will be necessary to be able implement this type of separation?

Welcome to aviation.SE! This question might have some useful information. The [tour] is a good way to learn more about how the site works.

this question is speculative. speculation are off topic as defined by the help center

There already is, to some extend.
Firstly, there is a big difference between separation in surveillance environments and non-radar environments. In non-radar environments, the separation minima are much larger, because separation is based on position reports provided by the aircraft, which is deemed less accurate than radar data.
In radar environments, the separation needed is generally 5 NM. However, in many terminal areas this is reduced to 3 NM - but only for aircraft going 250 KIAS or less (so, reduced relative speed). Moreover, on final approach, separation is commonly reduced to 2,5 NM - again, since the planes are going slow and pointing in the same direction (the runway), the relative speed is low.
Note that the navigation capabilities of individual aircraft does not matter, since separation is based on ground based equipment (radar), NOT on position information provided by the aircraft.

Thanks, I understand that, but in radar enviroment, is there any possibility to have dynamic longitudinal separations depending on the pair of aircraft in the future? eg: depending on the wake turbulence

@Paula Already exists. Wake turbulence separation minima range from 4 to 8 NM depending on the involved aircraft

If your question is prompted strictly by a concern for wake turbulence as one of your previous comments suggests, rest assured that Wake Turbulence Avoidance is already addressed in US pilot training and ATC procedures and protocol. Each aircraft is placed into a wake turbulence category. And both pilots and controllers follow specific rules of engagement depending on the traffic environment and aircraft involved. Pilots of light aircraft even have a safety out (3 minute separation cushion) when it comes to accepting takeoff clearance in a high wake turbulence environment.
As far as “ relative speed, navigation capacity of the aircraft, intersection geometry, etc.”, that is less of a concern in the terminal environment. For instance:

Relative speed is less of a concern when everyone except for hose in a Class B airspace must slow down below 200 knots when approaching an airfield’s airspace. Everyone below 10,000 feet must slow down below 250 knots. Anyone in a Class B airspace must fly at the speed assigned directly to them by ATC. If one is not assigned, they can not exceed 250 knots. And, everyone inside Class B airspace must be under the control of ATC. And any airfield with an operating control tower must give each aircraft their own individual clearances to use an IAP, join the traffic pattern, or to land.
Regardless of an aircraft’s means of navigation, all aircraft are roughly following the same basic routes and rules. Even an airplane flying on a route not specified has to follow specific altitude rules. And, communication protocols must be followed in all but uncontrolled airspace. Even then, protocols are highly recommended unless the aircraft does not have a means of communication.   Imagine multiple families going on the same road trip. Regardless of whether they all use a different means to get directions (Garmin, TomTom, Mapsco, Googlemaps on their phone, Waze, or their innate sense of direction and a list of landmarks), they should all arrive to their destination.
Except for airport environments where you are under direct ATC control, you are a small airplane in a big sky. In and around airfield’s airspace, training areas, victor airways, Navaids, etc., you are less likely to encounter another aircraft. In today’s age of GPS providing point-to-point direct routing, the use of victor airways and NavAids is less important. Giving rise to more open space to fly with less airway congestion. Regardless, you are required to practice extreme vigilance, monitoring the outside air to practice “See and Avoid” discipline.

The Airmen Information Manual has this to say about the subject...

7–3–9 Air Traffic Wake Turbulence Separations
a. Because of the possible effects of wake turbulence, controllers are required to apply no less than minimum required separation to all aircraft operating behind a Super or Heavy, and to Small aircraft operating behind a B757, when aircraft are IFR; VFR and receiving Class B, Class C, or TRSA airspace services; or VFR and being radar sequenced.

Separation is applied to aircraft operating directly behind a super or heavy at the same altitude or less than 1,000 feet below, and to small aircraft operating directly behind a B757 at the same altitude or less than 500 feet below:

(a) Heavy behind super—6 miles.
(b) Large behind super—7 miles.
(c) Small behind super—8 miles.
(d) Heavy behind heavy—4 miles.
(e) Small/large behind heavy—5 miles.
(f) Small behind B757—4 miles.

Also, separation, measured at the time the preceding aircraft is over the landing threshold, is provided to small aircraft:

(a) Small landing behind heavy—6 miles.
(b) Small landing behind large, non-B757 —4 miles.
Reference: Pilot/Controller Glossary—Aircraft Classes
b. Additionally, appropriate time or distance intervals are provided to departing aircraft when the departure will be from the same threshold, a parallel runway separated by less than 2,500 feet with less than 500 feet threshold stagger, or on a crossing runway and projected flight paths will cross:

Three minutes or the appropriate radar separation when takeoff will be behind a super aircraft;
Two minutes or the appropriate radar separation when takeoff will be behind a heavy aircraft.
Two minutes or the appropriate radar separation when a small aircraft will takeoff behind a B757.

Note: Controllers may not reduce or waive these intervals.
c. A 3-minute interval will be provided when a small aircraft will takeoff:

From an intersection on the same runway (same or opposite direction) behind a departing large aircraft (except B757), or
In the opposite direction on the same runway behind a large aircraft (except B757) takeoff or low/missed approach.

Note: This 3-minute interval may be waived upon specific pilot request.
d. A 3-minute interval will be provided when a small aircraft will takeoff:

From an intersection on the same runway (same or opposite direction) behind a departing B757, or
In the opposite direction on the same runway behind a B757 takeoff or low/missed approach.

Note: This 3-minute interval may not be waived.
e. A 4-minute interval will be provided for all aircraft taking off behind a super aircraft, and a 3-minute interval will be provided for all aircraft taking off behind a heavy aircraft when the operations are as described in subparagraphs b1 and b2 above, and are conducted on either the same runway or parallel runways separated by less than 2,500 feet. Controllers may not reduce or waive this interval.
f. Pilots may request additional separation (i.e., 2 minutes instead of 4 or 5 miles) for wake turbulence avoidance. This request should be made as soon as practical on ground control and at least before taxiing onto the runway.
Note: 14 CFR Section 91.3(a) states: “The pilot-in-command of an aircraft is directly responsible for and is the final authority as to the operation of that aircraft.”
g. Controllers may anticipate separation and need not withhold a takeoff clearance for an aircraft departing behind a large, heavy or super aircraft if there is reasonable assurance the required separation will exist when the departing aircraft starts takeoff roll.
Note: With the advent of new wake turbulence separation methodologies known as Wake Turbulence Recategorization, some of the requirements listed above may vary at facilities authorized to operate in accordance with Wake Turbulence Recategorization directives.


text:
Why do we take off with maximum power settings?
In most GA prop airplanes, take-off is executed with full throttle and high rpm. The usual reasoning is that this way, we leave the first few hundred feet, where failures are most severe, behind as fast as possible.
Isn't this like driving a car, seeing ice/playing kids/any other hazard, and speed up to leave the danger behind? In other words: Shouldn't we be most careful and conservative near the ground, with as little stress to the engine as feasible?

I used to actually do that in my plane when I used it to commute to work at an airport with a 10,000 ft runway.  Because I had 2 miles of runway ahead, plus all kinds of land-able terrain beyond, and I was flying alone with lots of reserve power, I adopted my own version of "flex thrust" and would just set climb power, about 24" of MP, and takeoff like that.  It's not a common practice outside of transport world however, and I would use normal takeoff power when departing regular GA airports.  On normal takeoffs I reduce power to climb settings at about 2-300 feet or so.

Aviation is an exercise in mitigating risks. There's usually more than one hazard at any given time.
So, yes, running your engine at full power might increase risk of engine failure versus a lower power setting.
However, taking off at lower power settings increases risks in other areas. For instance ...

... you have to reach rotation speed before you go flying, regardless of how long it takes to get to that speed. At lower power settings, you hit rotate speed closer to the departure end of the runway, so if you have an issue of some sort, you're more likely to run off the end of the runway.
... at lower power settings, you gain altitude slower and at a lower climb angle, so you have fewer options if the engine does give way.
... taking off with low power might hide the fact that you have an engine problem and can't make full power. You might not know your engine can't make full power until it's too late. (I've heard this was possibly factor in the recent B17 crash)

So, when you add all of the risks together, the industry has figured out that it's generally safer to take off at full power or close to it. That being said, a lot of operators do use lower power takeoffs to reduce wear and tear over time. Those that do this, however, only do it when it's relatively low-risk (long and dry runway, low takeoff weight, shallow obstacle clearance requirements, no difficult climb restrictions to make, etc).

It should come as no surprise that flying an airplane is not like driving a car. When driving a car, you can come to a complete stop and nothing exciting will happen. You cannot do this in an airplane; coming to a complete stop is either the beginning or the end of a great deal of excitement.
Flying near the ground in any circumstance is a hazard. As you say, the goal is to get away from the ground as quickly as possible. This should not be "stress to the engine", engines are designed and maintained to support the full throttle takeoff.

You bring up a good point in your last sentence - unlike most (not all*) car engines, aircraft engines will quite happily sit at a relatively high RPM for long periods of time. They are designed specifically for the task, and indeed can support fairly high periods of full throttle.
*As an example, the old VW aircooled engine had a cruise speed the same as its top speed. I doubt it's much of a coincedence that they shared a lot in common with the design of your average GA engine

Because Runways Are Short (relatively speaking)
The simple answer comes down to the fact that you only have so much space to take off so getting off the ground as fast as possible is the most practical and most safe option.
Aircraft will fly when the wings generate sufficient lift to overcome the weight of the aircraft, this happens when there is enough airflow over the wing which in turns broadly happens with sufficient air speed.
Lets examine a counter case for a minute. Say you did a partial power takeoff, you only apply some throttle (enough to overcome drag) and start your roll slowly, you will be out of runway long before you reach your takeoff speed. That being said with sufficiently long runways you would be able to take off with less than full power.
Aircraft engines have no issue spooling up and running at full power for takeoff and climb out, as a matter of fact aircraft engines are generally better at running at high power settings for long periods of time since that is exactly what they are designed for.
Takeoffs also include a "decision speed" which should take full throttle breaking distance into account so you should be able to abort a takeoff if there is insufficient power or speed.

But, also, the POH says so...

Not to mention that even if the runway is long enough to get off the ground in ground effect, your climb performance might not be good enough to clear the trees at the end of the airfield... so you may need high RPM anyway. And if the engine will quit at that power I'd rather that happen at 20kts on the ground than Vx at 50ft.

There are some exceptions, e.g. the turbo Arrow I fly will overboost at sea level with full throttle so we don’t go above 38" or so of MP.


text:
What is the format of data stored by a Flight Data Recorder?
Is the raw data fetched from the FDR available only in binary format and if so what are the software tools that are used to convert it to readable format?

This appears to be a duplicate of this question but it was closed and I'm not sure which one is more useful.

@Pondlife: It doesn't seem to me the other question asks for "what are the software tools that are used to convert it to readable format?", even if the titles are now similar.

@mins Good point, maybe it would be more accurate to just say "there's a lot of overlap here". That's not a big deal but I think it helps to point out similar questions, in case they already have a useful answer.

To simplify explanations:

FDR: flight data recorder (flight parameters),
DFDR: digital FDR,
CVR cockpit voice recorder (audio recording).

In commercial aircraft, aside the mandatory FDR/CVR used by investigation agencies (the scope of the question), there are recorders used for maintenance and operational purposes by the operator. The progress made around these additional recorders influences the regulation around the mandatory recorders.
Short answer to the questions:

Sensor data are collected by a central acquisition unit which, for commercial aircraft, is compliant to standards, e.g. a digital acquisition unit will be compliant to ARINC 717 and use the frame format from the standard.
Data are then distributed to other units under this format, this directly influences the format used by recorders. Today most FDR store data as bits in a digital memory or a on long term media (e.g. optical disc). The FDR required by regulation uses a crash-resistant digital memory.
Since a few years, recorded data format can be described using ARINC 647A specifications in an XML file, known as FRED file. This file simplifies FDR data exchange and interoperability, a current requirement for aircraft parameters monitoring and analysis using products from different manufacturers/editors.
A FRED file can also be stored along with data, and as a matter of fact, mandatory FDR regulation now requires the FRED file to be embedded in FDR.
Readout hardware/software is provided by the recorder manufacturer.

As mandatory and non-mandatory recorders from a given manufacturer are susceptible of using a common format, readout devices are usually combined with monitoring and data analysis software.
Details: Regulation
Quite surprisingly, there is no mandatory format for storing flight data. International regulations don't require or recommend a specific scheme. They only require data to be provided to the aeronautical authorities in a timely manner if an investigation has to be carried out after an incident/accident.
ICAO Chicago Convention, annex 6 states:

6.3.5.2 In approving the means to make flight recorder data available in a timely manner,
  the State of the Operator shall take into account the following:
a) the capabilities of the operator;
  b) overall capability of the aeroplane and its systems as certified by the
  State of Design;
  c) the reliability of the means to recover the appropriate CVR channels and
  appropriate FDR data;
  d) specific mitigation measures.

ICAO member States implement this international requirement, by requiring a documentation describing how data were calibrated and converted for recording and how to read them back. The related documents are known as Data Frame Layout and Conversion Data. E.g. for the US this is found in FAR 125.226:

Documentation sufficient to convert recorded data into the engineering
  units and discrete values specified in the applicable appendix must be
  maintained by the certificate holder.

and more details for DFDR in AC 20-141:

The data stream must be correlated to EU or to discrete states for an
  accident investigator to use the data.  This appendix provides the
  specific information that operators must provide to the NTSB
  investigators decoding and converting the raw data stream recorded by
  the DFDR.  This data format information can be contained within an
  electronic file or in hardcopy document format.

The description of the data frame layout and conversion method encompasses:

The origin of the recorded parameter, and any computation done
The method used for parameter calibration
The method used to encode the value of the parameter
The unit used.
The method to be used to convert recorded values into readable values.

In addition there are requirements about the certification of the mandatory recorders themselves, for most countries, the acceptable means of compliance directly or indirectly (e.g. via TSO-124 wrapper) refer to EurOCAE Document 112A (ED-112A) Minimum Operational Performance Specification for Crash Protected Airborne Recorder Systems.
Since 2016, ED-112A forbids the use of analog recorders, including magnetic tapes, for mandatory recorders. Non volatile solid state memory (EEPROM, typically Flash memory) is used instead.
More: What data file format is used by FDRs?
Recording format is influenced by the FDAU
Overall, data are recorded in any efficient format, not a user readable format. Data are compacted as much as possible to save memory and volume requirements of the crash survivable memory unit (CSMU), because of the cost of making this unit highly reliable and protected from the effects of an accident.
On large aircraft, parameters are collected by a flight data acquisition unit: Analog FDAU are compliant to ARINC 573 and digital DFDAU to ARINC 717). Digitalized data can be distributed to other avionics units using a local area network, e.g. the common ARINC 429 LAN. Units receiving data include cockpit displays, ACARS, and mandatory and non-mandatory recorders.

Is the raw data fetched from the FDR available only in binary format?

If we refer to large commercial aircraft, the answer is yes. Using ARINC 429 LAN already means data have been digitalized and streamed over the bus according to a well documented format. The FDAU choice greatly influences in practical how data will be recorded. It is easier to design a DFDR aligned on DFDAU ARINC 717 stream. ARINC 747 is an alternative with data compression for solid state memory.
ARINC 717 DFDR
The logical choice of the DFDR manufacturer is to use ARINC 717 both for a mandatory FDR and the various maintenance recorders. In this standard, the recorded data stream consists of a frame with four subframes.

Source
Each subframes is recorded at the rate of one per second, and contains a certain number of bits grouped into 12-bit words. The actual number of words depends on the need, hence on the aircraft. The cycle repeats after 4 seconds.
DFDR data example: Magnetic heading
Delays are to be taken into consideration, sensor output from the IRU takes some time to get to the recorder, this must be described by the manufacturer as part of the information needed for the recorded parameter readout:

Source CAP 731
Data transits on ARINC 429 bus identified by label 320, a BNR data:

Ibid
While no recording format is mandatory, the data sampling rate is critical: Transient values may be invisible if sampling is too slow. Therefore regulation mandates sampling rates.
A given parameter may appear only in some subframes, due to its sampling rate, and specific frames (superframes), recorded once per 64 seconds, are used for parameters which vary very slowly (e.g. gross mass). Examples of sampling rates:

Source
Data is recorded at some location in the overall framing of the FDR, this location is a choice of the DFDR manufacturer. For non-mandatory recorders (e.g. Quick Access Recorder, QAR) recorded parameters are chosen by the operator, as well as their location in the frames. For our example:

Ibid
Last but not least, the documentation describes how the recorded value must be processed to get the original parameter value and unit:
Heading Degree = 0.1758 x FDR Count (11 bit) - 180

Compliance to regulation
In spite of regulation, there are cases where data layout is unknown, e.g. BEA, the French investigation agency noted for a case:

The operator was not able to provide the BEA with any data
  frame layout documents. A list of recorded parameters and
  their allocation in the data frame was obtained, but the
  conversion equations and the calibration reports were missing.
  The FDR data could not be analyzed.

(Flight Data Recorder Read-Out, §2.3.2.1)
In the same document you may read other cases where the FDR data readout has been difficult or impossible.
The mandatory data frame layout and conversion method documents can be embedded into the FDR, to facilitate the readout and produce a file which can be understood by any compliant software. There is a standard for the documentation: The Flight Recorder Electronic Documentation (FRED) which is described in ARINC 647A.
There have been cases where the missing documentation prevented data interpretation (see below), but since 2016 and ED-112A, the FRED file must be carried in the recorder itself with the data, to ensure the data decoding.
FDR readout

What are the software tools that are used to convert it to readable format?

FDR manufacturers provide the tools required to read out data, based on their own recording techniques. Readout is done using simple hardware/software.
Readout is facilitated by reusing the embedded FRED file or using an external file (a FRED file is an XML file describing in detail the way the recording was done, and the format used):

Source: ARINC 647A
It should be noted manufacturers usually also sell non mandatory recorders (QAR and the many variants of QAR) and they provide not only readout tools, but also analysis/monitoring tools. Example:

ROSE analysis unit, source
Other readout solutions:

KGB Aviation
ATM

You can see the FDR itself is used for the readout. In case the FDR unit is broken (which is frequent after accidents), the protected memory unit is extracted and read with another working FDR.
Extraction of the memory module protected in temperature resistant foam:

(Source: ATSB accident report)
Readout facilities and readout certification
FDR/CVR readout cannot be trusted unless it's done with appropriate knowledge, skills and documentation. This is the reason readouts used by official agencies, which can be used at courts to try determining responsibilities after an accident, are required to be done by certified personnel in approved facilities.

If "data are compacted as much as possible", it would be difficult to recover it if a small part of it is damaged (try to change a single bit in a jpeg!) I never heard of any advanced compression method used for FDR/CVR. Do you know of any examples?

@Zeus: I didn't mentioned compression (just using the number of bits which are necessary, given the range of values and the resolution), but that's not a problem per se either, as there are efficient correcting codes for low signal/noise ratio. I added a mention to ARINC 747, a standard for compression on Flash RAM.